Advances in the use of induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM) have dramatically advanced the study of heritable human genetic cardiac diseases. While these advances will eventually lead to new treatment options and improved patient counseling, these cellular model systems also permit mechanistic insights and provide a platform for modeling human cardiac tissues. The latter is critically important as patients with cardiomyopathies (genetic and non-genetic forms) or heart failure often experience arrhythmias that can result in sudden death. To study the predisposition of genetic disease syndromes to cause arrhythmias in cardiac tissue, iPSC-CMs will be cultivated in engineered heart slices (EHS), developed by our team that recapitulate a natural 3D microenvironment and enable electromechanical interactions among cells and the extracellular matrix. Our EHS support the growth of engrafted iPSC-CMs; provide important topological, biochemical, and mechanical signals to the cells; manifest functional tissue behavior, including coordinated electrophysiological and contractile activity; and can sustain cardiac arrhythmias in a quantifiable manner. In this project, we propose to use EHS to investigate mechanisms underlying the manifestation and progression of arrhythmias that promote sudden death. As a genetic tool for modeling arrhythmias, we will study iPSCs generated from probands of arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVC) that affect proteins of the cardiac desmosome. In patients, this disease is highly pro-arrhythmic and can lead to sudden cardiac death in young athletes. Hence, the goal of this project is to investigate how structural defects promote arrhythmias in EHS. Specifically we will determine if 1) mutations of desmosomal proteins operate in the early concealed phase of AC to impair intercellular mechanical coupling, resulting in abnormal electrical coupling, slowing of electrical conduction, and reentrant arrhythmia, and 2) secondary alterations in sodium channel function also result in slowing of electrical conduction and arrhythmia. The project involves three complementary and related Aims. Aim 1 will examine the importance of syncytial interactions and tissue microenvironment on the expression and progression of the disease phenotype in ARVC iPSC-CMs. Aim 2 will develop models of simulated exercise to determine increased risk of arrhythmia in EHS models of ARVC. Aim 3 will investigate the instructive cues of different native, extracellular matrices on cellular remodeling and tissue- level arrhythmia in EHS models of ARVC. The outcome of this research will shed light on mechanisms of arrhythmia and sudden cardiac death associated with abnormalities of mechanical junctions that operate not only in ARVC but also in other more common forms of cardiomyopathies. Our study on tissue microenvironment and disease progression in the cardiomyocyte represents a critical step towards the identification of primary and ancillary pro-arrhythmic disease pathways that may prove invaluable to the development of new therapies designed to treat heritable cardiac diseases.